In citizens band radio applications the ideal antenna is a full quarter wavelength vertical radiator (about 8 1/2 feet long at about 27 MHz). However, most of these antennas are carried on automobiles and it would be impractical to carry an antenna over eight feet in length. This has been recognized in the prior art and as a result a shortened so-called "loaded" antenna has been used. The loading apparatus is placed at a base which is mounted on the vehicle, and the base supports a shortened antenna commonly referred to as an "antenna whip".
Shortening an antenna to a length of less than a quarter wavelength transforms the radiator from an almost purely resistive device that closely matches its associated transmission line to a device having resistance and capacitive reactance. The simplest means of offsetting this added capacitive reactance is to place a cancelling inductive reactance into the transmission line radiator circuit. This use of a coil, or inductive reactance, is commonly known in the art as "loading". The coil of wire is wound on a support and placed along the shortened radiator, often at the base which is mounted on the vehicle.
Prior art designs for citizen band antennas have lacked efficiency due largely to losses incurred in the loading coil. It is well understood that inductive elements are subjected to capacitive losses such as from the capacitance effects between turns of the coil. What is perhaps less well understood is the nature and cause of so-called dielectric losses, which occur within the insulating materials used to support coils. Such dielectric losses manifest themselves primarily as heat, which limits the power-handling capacity of the antenna as well as reducing efficiency.
Commercial antennas used for citizen band application have generally not been used also for amateur radio. A primary reason is that the coils of most currently available citizen band antennas are designed for low power use (e.g., 5 watts), and would burn out if used at the power levels that are common in amateur radio (e.g., up to 1000 watts). However, there is an obvious advantage to being able to use the same antenna for both applications for those who are involved in both types of radio communications.